CN115326601B - Dynamic impact test and evaluation method for anchor net coupled supporting rock mass - Google Patents
Dynamic impact test and evaluation method for anchor net coupled supporting rock mass Download PDFInfo
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Abstract
The invention provides an anchor net coupling support rock mass dynamic impact test and evaluation method, and relates to the field of rock mechanics. Aiming at the problem that the shock resistance of the conventional anchor rod and anchor net coupled supporting rock mass is inconvenient to obtain, a coupled rock mass sample with the anchor rod and anchor net arranged is subjected to a high-strain-rate impact test, and a corresponding monitoring assembly is configured to monitor the impact test process, so that evaluation indexes of surface strain, crack evolution characteristics, rock mass destruction strength, anchor rod deformation, energy absorption capacity improvement coefficient and rock mass debris distribution characteristics of the rock mass are established, and the rock mass anchoring effect under the dynamic impact condition is evaluated. The method comprises the following specific steps: arranging an anchor net and an anchor rod on a non-impact surface of the cubic rock mass test piece, pre-tightening, spraying speckles on the surface of the test piece, and obtaining a coupling test piece; arranging a monitoring assembly on the coupling test piece, and applying high-strain-rate impact load; acquiring data of the coupling test piece under impact through a monitoring assembly, and collecting rock mass debris; and processing and analyzing the acquired data, and evaluating the anchoring effect according to the indexes.
Description
Technical Field
The invention relates to the field of rock mechanics, in particular to a dynamic impact test and evaluation method for an anchor net coupling supporting rock mass.
Background
With the continuous increase of the mining depth of coal resources, deep engineering disasters such as rock burst, large deformation of surrounding rocks of a roadway and the like are increased day by day, and great threat is brought to the efficient mining of deep resources. Rock burst is a dynamic disaster in which elastic deformation energy gathered by a rock body on a working face is suddenly released to generate strong vibration and cause severe damage to the rock body.
The anchor rod (cable) -net coupling support is an economic and effective support mode, the anchor net can convert point load of pre-tightening force of the anchor rod (cable) into surface load, the effective area of active support is enlarged, the self-supporting capacity of surrounding rock is improved, and therefore the capacity of the surrounding rock for resisting dynamic disturbance and impact is improved. In order to test the impact resistance of the coupled anchor rods and anchor nets, a testing device capable of simulating the severe damage phenomenon and process of the supported rock mass is needed. The existing laboratory test equipment fixes one end of an anchor rod, and directly applies impact load to the other end of the anchor rod, so that the actually measured impact resistance of the anchor rod comprises the energy absorbed by the tensile elongation of the whole length of the anchor rod, the test result is greatly different from the site characteristics of the anchor rod, the existing test equipment cannot truly reflect the interaction between an anchor rod net and surrounding rock, namely, the impact load borne by the anchor rod net is inconsistent with the actual site condition, and the reinforcement effect of an anchor rod net coupling body on the surrounding rock under the action of the impact load cannot be directly reflected, meanwhile, the rock mass is damaged at high strain rate when being severely damaged, the dynamic test of the anchor rod net coupling support rock mass at high strain rate is difficult to carry out, a corresponding test method is lacked, and the mechanism of the mutual coupling action between the anchor rod net and the rock mass is difficult to obtain.
Disclosure of Invention
The invention aims to provide a dynamic impact test and evaluation method of an anchor net coupling supporting rock mass, aiming at the defects in the prior art.
The dynamic impact test and evaluation method for the anchor net coupling supporting rock adopts the following scheme:
the method comprises the following steps:
arranging an anchor net and an anchor rod on a non-impact surface of the cubic rock mass test piece, pre-tightening, and spraying speckles on the surface of the test piece to obtain a coupling test piece;
arranging a monitoring assembly on the coupling test piece, and applying a high-strain-rate impact load;
acquiring data of the coupling test piece under impact through the monitoring assembly, and collecting rock mass debris;
processing and analyzing the acquired data, and evaluating the anchoring effect according to the indexes;
wherein, anchor effect index includes: the method comprises the following steps of (1) rock mass surface strain, crack evolution characteristics, rock mass destruction strength, anchor rod deformation, energy absorption capacity improvement coefficient and rock mass debris distribution characteristics.
Further, the anchor rods are arranged at four corners of the side face of the test piece, the anchor rods penetrating through the test piece are arranged at the four corners of the side face of the test piece respectively, and pre-tightening force is applied to the anchor rods after the anchor nets are arranged.
Further, the anchor net is continuously arranged around the non-impact surface of the test piece, wraps the test piece and avoids the anchor rod, and pressure monitoring elements are installed at the two ends of the anchor rod.
Furthermore, the pretightening force of the anchor rod on the test piece can be adjusted, different pretightening forces are configured for different samples to respectively obtain impact test data, and the impact resistance of the samples under different pretightening forces is contrastingly analyzed.
Furthermore, the monitoring assembly comprises a pressure monitoring element, a stress-strain monitoring element, a displacement monitoring element and an image acquisition element; the pressure monitoring component is arranged in the stock, and the stress-strain monitoring component is arranged in the coupling test piece, and the displacement monitoring component is arranged in the coupling test piece side to monitoring rock mass, anchor net and stock displacement, image acquisition component obtain the image when impact test.
Further, correlation calculation is carried out on the speckle image gray levels before and after the surface of the coupling test piece deforms, displacement and strain parameters of the test piece are obtained, and the surface strain distribution of the rock mass of the coupling test piece is calculated.
Further, a box dimension method is adopted for measurement, square grids of different code scales are adopted to cover the measured area, the code scales of the grids are given, the number of the grids needed by the coverage image is calculated, fitting is carried out to obtain the fractal dimension of the rock cracks, and the crack evolution characteristics are calculated.
Further, monitoring by using a dynamic pressure sensor arranged on the anchor rod to obtain a curve of pressure changing along with time, and defining a curve peak point as rock destruction strength; and measuring the displacement of the anchor rod in real time by using a laser extensometer, and calculating the elongation of the anchor rod to obtain the deformation of the anchor rod.
Further, respectively calculating the energy absorbed by the coupling test piece and the energy absorbed by the non-supporting rock test piece, wherein the energy absorption capacity improvement coefficient is equal to the ratio of the total energy absorbed by the coupling test piece to the total energy absorbed by the non-supporting rock test piece;
screening the fragments of the damaged anchor net coupling support rock mass according to the particle size to obtain multiple groups of fragments with different particle sizes, and calculating the ratio of the mass of each group of fragments to the total mass.
Further, the evaluation comprises the steps of:
carrying out standardization processing on each evaluation index;
calculating the weight of each index by adopting an subjective and objective comprehensive weighting method;
and evaluating the rock mass anchoring effect by using a fuzzy comprehensive evaluation method.
Compared with the prior art, the invention has the advantages and positive effects that:
(1) Aiming at the problem that the shock resistance of the existing anchor rod and anchor net coupling supporting rock mass is inconvenient to obtain, the high-strain-rate impact test is carried out on the coupling rock mass sample with the anchor rod and anchor net, a corresponding monitoring assembly is configured to monitor the impact test process, evaluation indexes are set to evaluate the processed parameters, the site working condition is simulated, and the shock resistance of the coupling sample is obtained.
(2) According to six indexes of surface strain distribution, crack fractal dimension, rock destruction strength, anchor rod axial deformation, energy absorption capacity improvement coefficient and rock mass debris distribution characteristics of the anchor net coupling support rock mass, the weight of each index is obtained by adopting an 'analytic hierarchy process + entropy weight method' subjective and objective comprehensive weighting method, the rock mass anchoring effect is evaluated by utilizing a fuzzy comprehensive evaluation method, and the action mechanism between the anchor rod and anchor net coupling body and the rock mass is researched in an auxiliary mode.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are included to illustrate an exemplary embodiment of the invention and not to limit the invention.
Fig. 1 is a flowchart of a dynamic impact test and evaluation method of an anchor net coupled timbering rock mass in embodiment 1 of the invention.
Fig. 2 is a schematic diagram of the anchor net coupling supporting rock mass impact test equipment in embodiment 1 of the invention.
Fig. 3 is a schematic diagram of an anchor net coupled rock mass test piece in embodiment 1 of the invention.
Fig. 4 is a schematic view of an anchor net coupling supporting rock mass anchoring effect evaluation hierarchical structure model in embodiment 1 of the present invention.
In the figure, 1 Hopkinson power loading system; 2. a bullet; 3. a laser tachometer; 4. an incident rod; 5. a protective cover; 6, a camera; 7. coupling a test piece; 8. a transmission rod; 9. a laser extensometer; 10. a strain gauge; 11. a tray; 12. a lock; 13. a dynamic pressure sensor; 14. an anchor rod; 15. a rock mass test piece impact surface; 16. a rock mass test piece; 17. and (6) anchoring the net.
Detailed Description
Example 1
In an exemplary embodiment of the invention, as shown in fig. 1-4, a dynamic impact test and evaluation method for an anchor net coupled supporting rock mass is provided.
The method comprises the following steps: preparing a cubic rock mass test piece 16 according to rock mass dynamics test standards, drilling the rock mass test piece 16, drilling a hole vertical to a rock surface, drilling and penetrating the test piece, and then introducing an anchor rod 14 and an anchoring agent into the drilled hole. And after the anchoring agent is solidified, paving an anchor net 17, sequentially installing the tray 11, the lock 12 and the dynamic pressure sensor 13, applying pretightening force, spraying speckles on the surface of the rock mass, and completing the coupling and supporting of the anchor rod 14 and the anchor net 17 on the rock mass to obtain the coupling test piece 7.
Step two: arranging a coupling test piece 7 in a Hopkinson power loading system 1, arranging a protective cover 5, clamping the coupling test piece 7 between an incident rod 4 and a transmission rod 8, sticking a strain gauge 10 on the incident rod 4 and the transmission rod 8, connecting the strain gauge 10 with a super-dynamic strain gauge, and starting an impact test after the instrument is debugged.
Step three: and a laser velocimeter 3 is arranged between the Hopkinson pressure bar and the impact bar to measure the speed of the bullet 2.
Step four: high-pressure gas is as assaulting the power supply, and inlay in the gas vent of compressed air chamber in the launching tube, and in the launching tube was placed in bullet 2, release high-pressure gas drive bullet 2 acted on the pole 4 that incites, and the pole 4 that incites acts on rock mass test piece impact face 15, accomplishes the power and assaults the loading.
Step five: and recording data such as stress, strain, displacement and the like of the coupling test piece 7 under the dynamic impact condition by using a monitoring system. After the test is completed, rock mass debris is collected.
Step six: and evaluating the rock mass anchoring effect by integrating the rock mass surface strain, the crack evolution characteristic, the rock mass destruction strength, the anchor rod 14 deformation, the energy absorption capacity improvement coefficient and the rock mass debris distribution characteristic.
As shown in fig. 1 and 3, drilling a rock mass test piece 16 in the first step, wherein the diameter of the drilled hole is slightly larger than the diameter of the anchor rod 14 material, so that the anchor rod 14 and the tray 11 can be reasonably installed, and the four drilled holes are arranged in a square shape, so that the anchor net 17 material is reasonably fixed.
Meanwhile, as shown in fig. 3, the anchor net 17 material in the first step is laid, firstly, the anchor net 17 material with a proper size is manufactured, the width of the anchor net 17 is equal to that of the non-impact surface, the anchor net 17 is tightly wrapped around the rock body from the rock surface of the drilled hole, then, the anchor rod 14 material penetrates through the anchor net 17 and the rock body test piece 16, and the tray 11, the dynamic pressure sensor 13 and the lock 12 are sequentially installed at the two ends to form the anchor net coupling supporting rock body.
The anchor rods 14 and the anchor nets 17 of the anchor net coupling supporting rock body are made of ideal elastic-plastic materials, and have the characteristics of high prestress, high constant resistance, high energy absorption and high elongation. The anchoring material includes NPR (Negative Poisson Ratio) material, TWIP (Twinning Induced Plasticity Steel) high-strength high-toughness material, and other ideal plastic materials.
It should be noted that the pre-tightening force of the anchor rod 14 on the test piece can be adjusted, different pre-tightening forces are configured for different samples to respectively obtain impact test data, and the impact resistance of the samples under different pre-tightening forces are contrastively analyzed; similarly, for the anchor rod 14 and the anchor net 17, the anchoring materials with different length specifications and different diameter specifications can be configured for different samples, and also can be configured for different materials, and similarly, test data is respectively obtained for the anchoring materials under different configurations, and the impact resistance of the samples under different configurations is contrastively analyzed.
In addition, drilling parameters on the rock mass test piece 16 can be adjusted, drilling holes with different quantities, different intervals, different arrangements and different apertures are configured for different samples, impact test data are respectively obtained, and the impact resistance of the samples under different drilling hole configurations is analyzed.
As shown in fig. 1 and 2, the monitoring assembly includes a pressure monitoring element, a stress-strain monitoring element, a displacement monitoring element, and a high-speed camera system. The pressure monitoring element consists of a dynamic pressure sensor 13 and a charge amplifier, and the stress-strain monitoring element consists of a strain gauge 10 and a dynamic strain acquisition instrument. The displacement monitoring element is composed of a laser extensometer 9, is perpendicular to the impact direction and is arranged on one side of the coupling test piece 7, and monitors the displacement of the rock mass test piece 16, the anchor net 17 and the anchor rod 14.
The pressure monitoring element is arranged on the anchor rod 14, the stress-strain monitoring element is arranged on the coupling test piece 7, the image acquisition element acquires an image during the impact test, and the image acquisition element can adopt the high-speed camera 6.
As shown in fig. 1, the strain distribution of the surface of the coupling test piece 7 is calculated.
And performing correlation calculation on the gray levels of the speckle images before and after the surface of the test piece is deformed by using a digital image correlation method, so as to obtain parameters such as displacement, strain and the like of the test piece. Firstly, calculating correlation coefficients of all points in a certain range on a deformed image and an image reference point before deformation, and then taking the point with the maximum correlation coefficient as a target point. On the basis, the displacement before and after deformation can be obtained by calculating the coordinate difference value of the reference point and the target point, and further the strain of the rock mass is calculated.
As shown in fig. 1, the fractal dimension of the surface crack of the coupling specimen 7 was calculated.
The fractal dimension characterizes the irregularity and complexity of the crack pattern. The fractal dimension of the rock mass cracks is measured by adopting a box dimension method, square grids (a x a) of different code scales are adopted to cover a measured area, the code scale of a given grid can calculate the number of grids required by a coverage image, and then fitting is carried out.
In the formula (I), the compound is shown in the specification,ais a code ruler of a square grid,N(a)for the corresponding number of the squares,Dis the dimension of the box and is,Aare the corresponding coefficients.
As shown in fig. 1, the breaking strength of the coupling test piece 7 was calculated.
And monitoring by using a dynamic pressure sensor 13 to obtain a pressure change curve along with time, and defining a curve peak point as rock destruction strength.
As shown in fig. 1, the axial deformation of the bolt 14 is calculated.
The displacement of the anchor rod 14 is measured in real time by the laser extensometer 9, and the elongation of the anchor rod 14 is calculated.
As shown in fig. 1, the energy absorbing capacity improvement coefficient was calculated.
Obtaining the axial force of the anchor rod 14 through the dynamic pressure sensor 13FOver timetBy the laser extensometer 9, the deformation of the anchor rod 14 is obtainedxOver timetThereby obtaining the axial forceF=f(x) The change curve along with the deformation of the displacement further obtains the energy absorbed by the anchor rod 14 in the impact processΔE B ，
In the formulaΔE B For the impact energy absorbed by the anchor rods 14,Sfor the final displacement of the anchor rods 14,f(x)in order to provide an axial force to the anchor rods 14,xis the displacement deformation of the anchor rod 14.
The law of conservation of energy is beneficial to knowing:
in the formulaΔE tot In order to couple the total absorbed energy of the test piece 7,ΔE B for the impact energy absorbed by the anchor rods 14,ΔE R the impact energy absorbed by the rock mass,ΔE W for the impact energy absorbed by the anchor net 17,O(ΔE)is micro energy dissipated in other forms such as heat energy, sound energy and the like in the impact process,mthe mass of the bullet 2 is the mass of the bullet,vthe initial velocity of the bullet.
Obtaining the initial velocity of the bullet 2 through a laser tachometer, and calculating by combining the mass of the rock to obtain the impact energy absorbed by the coupling test piece 7ΔE tot 。
Further solving the energy absorption rate of the anchor rod 14ηEnergy absorbed for the bolt 14ΔE B Total absorbed energy of coupling test piece 7ΔE tot Percentage of the ratio.
By comparing the total absorbed energy of the non-supporting rock mass under dynamic impactΔE non And the coefficient of improving the coupling energy absorption capacity of the anchor net 17 is establishedαAnchor net 17 coupling energy absorption capacity improvement factorαEqual to the energy absorbed by the coupling coupon 7ΔE tot Energy absorbed by non-support rock mass test pieceΔE non The percentage of the ratio is as follows:
as shown in fig. 1, the debris distribution characteristics of the coupling coupon 7 are calculated.
And screening the broken chips of the coupling test piece 7, and dividing the sizes of the particles into 4 groups of coarse-particle chips (the particle size is larger than 30 mm), medium-particle chips (5 to 30mm), fine-particle chips (0.075 to 5 mm) and fine-particle chips (< 0.075 mm). And weighing the mass of the rock mass scraps sieved out of each grain group, and calculating the ratio of the mass of each grain group scraps to the total mass.
As shown in fig. 4, firstly, the six indexes of the surface strain distribution, the crack fractal dimension, the rock destruction strength, the axial deformation of the anchor rod 14, the energy absorption capacity improvement coefficient and the rock debris distribution characteristic of the coupling test piece 7 are standardized.
Secondly, the weights of all indexes are obtained by adopting an subjective and objective comprehensive weighting method of an analytic hierarchy process and an entropy weight method.
The proportion of various indexes is determined by introducing expert practical experience through an analytic hierarchy processw aj . Taking the rock mass anchoring effect as a target layer of the hierarchical analysis, taking excellent, good, qualified and unqualified rock mass anchoring effect as a scheme layer, taking the surface average strain, the crack fractal dimension, the rock mass destruction strength, the elongation of the anchor rod 14, the energy absorption capacity improvement coefficient and the mass ratio of fragments with different particle diameters as a criterion layer, and constructing a rock mass anchoring effect evaluation hierarchical structure model.
In order to make up for the subjectivity of the analytic hierarchy process, the entropy weight method is used to determine the weights of various indexesw bj . Combining the weight calculation results of the two methods, and providing the comprehensive weight of the indexw j The expression is as follows:
in the formula:a-weightw aj The coefficient of (a);b-weightw bj The coefficient of (a);w aj weights are obtained for the analytic hierarchy process;w bj weights are found for the entropy method.
And finally, evaluating the rock mass anchoring effect by using a fuzzy comprehensive evaluation method.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. The dynamic impact test and evaluation method of the anchor net coupled supporting rock mass is characterized by comprising the following steps:
arranging an anchor net and an anchor rod on a non-impact surface of the cubic rock mass test piece, pre-tightening, spraying speckles on the surface of the test piece, and obtaining a coupling test piece;
arranging a monitoring assembly on the coupling test piece, and applying a high-strain-rate impact load;
acquiring data of the coupling test piece under impact through the monitoring assembly, and collecting rock mass debris;
processing and analyzing the acquired data, and evaluating the anchoring effect according to the indexes;
wherein, the anchor effect index includes: the surface strain of the rock mass, the crack evolution characteristic, the rock mass destruction strength, the deformation of the anchor rod, the energy absorption capacity improvement coefficient and the rock mass debris distribution characteristic;
the anchor rods are arranged at four corners of the side surface of the test piece, the four corners of the side surface are respectively provided with the anchor rods penetrating through the test piece, and pre-tightening force is applied to the anchor rods after the anchor nets are arranged; the anchor net is continuously arranged around the non-impact surface of the test piece, wraps the test piece and avoids the anchor rod, and pressure monitoring elements are arranged at two ends of the anchor rod;
the evaluation comprises the following steps:
carrying out standardization treatment on each evaluation index;
calculating the weight of each index by adopting an subjective and objective comprehensive weighting method;
and evaluating the rock mass anchoring effect by using a fuzzy comprehensive evaluation method.
2. The dynamic impact test and evaluation method for the anchor net coupled and supported rock mass according to claim 1, wherein the pre-tightening force of the anchor rods on the test piece is adjustable, different pre-tightening forces are configured for different samples to respectively obtain impact test data, and the impact resistance of the samples under different pre-tightening forces is contrastively analyzed.
3. The dynamic impact test and evaluation method for the anchor net coupled supporting rock body according to claim 1, wherein the monitoring assembly comprises a pressure monitoring element, a stress-strain monitoring element, a displacement monitoring element and an image acquisition element; the pressure monitoring component is arranged in the stock, and the stress-strain monitoring component is arranged in the coupling test piece, and the displacement monitoring component is arranged in the coupling test piece side to monitoring rock mass, anchor net and stock displacement, image acquisition component obtain the image when impact test.
4. The method for testing and evaluating dynamic impact of an anchor net coupled supporting rock mass according to claim 1, characterized by performing correlation calculation on the speckle image gray levels before and after the surface of the coupling test piece is deformed to obtain the displacement and strain parameters of the test piece and calculate the strain distribution on the surface of the coupling test piece rock mass.
5. The dynamic impact test and evaluation method of the anchor net coupled timbering rock mass according to claim 1, characterized in that the measurement is performed by a box-dimension method, square lattices with different yardsticks are adopted to cover the measured area, the yardstick of the lattice is given and the number of the squares required for covering the image is calculated, fitting is performed to obtain the fractal dimension of the rock cracks, and the crack evolution characteristics are calculated.
6. The method for testing and evaluating the dynamic impact of the anchor net coupled support rock mass according to claim 1, characterized in that a curve of pressure variation with time is obtained by monitoring with a dynamic pressure sensor arranged on the anchor rod, and a peak point of the curve is defined as the destruction strength of the rock mass; and measuring the displacement of the anchor rod in real time by using a laser extensometer, and calculating the elongation of the anchor rod to obtain the deformation of the anchor rod.
7. The method for testing and evaluating dynamic impact of an anchor net coupled timbering rock mass according to claim 1, wherein the energy absorbed by the coupled test piece and the energy absorbed by the non-timbering rock mass test piece are calculated respectively, and the energy absorption capacity improvement coefficient is equal to the ratio of the total energy absorbed by the coupled test piece to the total energy absorbed by the non-timbering rock mass test piece;
and screening the fragments of the damaged anchor net coupling support rock mass according to the particle size to obtain multiple groups of fragments with different particle sizes, and calculating the ratio of the mass of each group of fragments to the total mass.
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| CN117272457B (en) * | 2023-09-07 | 2024-06-07 | 山东高速基础设施建设有限公司 | Comprehensive evaluation method for highway tunnel supporting system |
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| CN110274831B (en) * | 2019-07-05 | 2020-07-07 | 山东科技大学 | Device and method for testing anchor rod (cable) supporting structure and comprehensively testing performance of anchor system |
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